Process of electrolytically depositing iron and nickel alloy



Patented Sept. 2 7, 1938 I'l'lNG IRON William A. Crowder, Newark, N. 1., m.- to

Pyrene Manufacturing Company, Newark,

N. 1., a corporation'of Delaware No application-Nov mber 19'. 'ms,

. 5 Claims. The present invention relates in general to electrodeposition of metals, and has for an object: to produce homogeneous depositsof iron and nickel alloy not substantially exceeding 5% 5 nickel.

Another object of the invention is to produce deposits of iron and nickel not substantially ex- 1 ceeding 5% nickel alloyed in definite proportions, i. e., in the proportions in which these metals it) are present in the-solution from which the de-- posits are produced.

Still another object of the invention is toproduce deposits of iron and nickel alloy not substantially exceeding 5% nickel in ductile form,

15 i. e., in a form which can be machined as it leaves the electrolyte withou In accordance with objects are attained by the use of an electrolyte having several important operating character- 80 istics, all of which will hereinafter appear.

prior, annealing.

The deposits produced from this electrolyte,

besides their homogeneity, ductility, and capability of production in definite proportions of iron and nickel, are of a. suitable crystal structure 25 that will firmly adhere to the base metal as is necessary in building up worn machine parts, and may be satisfactorily produced on -aluir'iinum,

aluminum alloys, cast iron, zinc, zinc alloys, lead,

lead alloys, steel, copper, brass, and graphite or 80 carbon surfaces, for the purpose of electroforming and for use as a base for other types plating. Moreover, they may be satisfactorily produced for electroforming of tubes, cylinders or other parts requiring high tensile strength, de-

so posits containing as muchas nickel being permitted by the invention.

In accordance with the process oi? the present invention, iron and nickel alloy not substantially exceeding 5% nickel is electrodeposited through.

49 a heated solution offerrous sulphate and nickel sulphate, in which solution hydrofluoric acid and sodium fluoride are both present. Preferably the hydrofluoric acid is formed in 'situ by causing part of the sodium fluoride to react with sulphuric being also formed by the 45 acid, sodium sulphate reaction shown in the following equation:

fissos+2NaF=Naasoa+2m In preparing the solution, ferrous sulphate and 50 nickel sulphate are employed in. such relative quantities as to cause the ratio of nickel to iron tov be the same as in the desired alloy not substan-- tially exceeding 5% nickel tobe deposited. The

quantity of hydrofluoric acid to be either added 55 or formed in situ should be such as to cause the the invention, the above a solution to be operated at a pH not exceeding 5.0, preferably at a pH between 3.0 and 5.0. The quantity of sodium fluoride should be such asto cause the solution to be substantially saturated therewith. For producing the hydrofluoric acid in situ, the sodium fluoride should be in excess of the quantity required for its reaction (with sulphuric acid), theexcess being such as-to enable such saturation to be obtained.

The preferred temperature of operation of the solution is substantially 70 centigrade, above which the solution need not be heated for its satisfactory operation, maximum solubility of ferrous sulphate being reached at 70 centigrade.

Preferably, ferrous sulphate should. be em- "ployed in quantity suflicient to bring the solution. at the temperature of operation, to a specific gravity of substantially 1.25 (referred to water at 20 centigrade). Analysis oi the iron content of the solution is then made, and nickel sulphate is added in the amount corres nding to the desired alloy not substantially exceeding 5% nickel to be deposited, the usual amount added being suchas to produce'an alloy of from 3% to 5% nickel, which range conforms with specifications for nickel steel of high tensile strength. At the stated spending to 8. to fluoride and approximately 2 cubic centimeters of concentrated sulphuric acid (66'' Baum),

specific gravity of 1.25 (referred both per litre of water, have been found satisfactory for producing the hydrofluoric acid in situ. With-the sodium fluoride and sulphuric acid employed in such amounts, the hydrofluoric .acid formed by reaction is the principal agent effectinganode corrosion during electrolysis. That is, itsis the hydrofluoric acid, andnot so much the sulphuric acid, which causes the iron and nickel 'at the anodes to pass into solution. The sodium fluoride and sulphuric acid should both be added prior to the ferrous sulphate and nickel sulphate. I

If the nickel contentof the solution does not exceed the limit permitted by the invention (corresponding to an alloy not substantially exceeding' 5% nickel), iron and nickel are deposited at the cathode substantially in the same ratio as these metals occur in the solution. This is deemed one of the important aspects oi the in-- 1 vention and has be'aniound to be due to the use of hydrofluoric acid and sodium fluoride in the solution, particularly when that acid. is formed in situ. It is quite possible that a complex salt of iron (ferrous fluorosulphate) and a complex preferred solution concentration corre water at 20 centigrade), 25 grams of sodium salt of nickel (nickel fluorosuiphate) are produced in the solution, which salts may act to effect the equalization of the cathode potentials with respect to the iron and nickel in solution, enabling these metals to be deposited in any ratio of nickel to iron deslred'no greater than the limit contemplated by the invention (corresponding to an alloy not substantially exceeding 5% nickel).

Another important feature of the invention resides in the stated preferred solution concentration corresponding to a specific gravity of 1.25 (referred to water at centigrade) which concentration is exceptionally high and is made possible essentially by the high activity of fluorine, which-prevents passivity at the concentration, it has been found that the osmotic pressure in the solution is such asto insure its most satisfactory operation. Substantially constant conditions are maintained in the solution, secondary anode corrosion being reduced to a minimum. That is. little iron and nickel are dissolved at the anode when the solution is not in service, and little iron and nickel over the amounts necessary to produce the deposit at the cathode are dissolved under operating conditions. This even and quantitative solution at the anodes at a. concentration corresponding to a specific gravity of 1.25 (referred to water at 20 centisrade) acts to maintain the solution at that concentration.

The stated preferred solution concentration corresponding to a specific gravity of 1.25 (referred to water at 20 centigrade) is a critical value. Thus, ifat the temperature of operation the concentration of the solution is reduced to, say, the degree corresponding to a specific gravity of 1.2 (referred to water at 20 centigrade). the osmotic pressure is correspondingly reduced to a point where too rapid anode corrosion takes place, thereby causing rapid changes in the acidity of the solution, which in turn not only necessitates pH measurements atshort intervals, but also exerts a detrimental effect on the ductility of. the

deposit. 11,011 the other hand, at the temperature of operation the concentration of the solu-. tlon is increased to. say. the degree corresponding to the specific gravity of 1.3 (referred to water at 20 'centigrade) the osmotic pressure is increased to a point where all anode corrosion substantially ceases, which not only increases the acidity of the solution, but also lowers the cathode emciency or rate of deposit at the cathode, the depot here again being adversely affected in charac r. a

At the stated preferred solution concentration corresponding to a specific gravity of 1.25 (referred to water at 20 centigrade), the large amount of ferrous sulphate in the solution renders itextremely conductive to electric current. The solution may thus be satisfactorily operated employing current densities as high as from 15 to 30 amperes per square decimeter. At these high current densities the rate of deposit is considerably accelerated, and the'tendency toward tree-1 ing or rough depoflts is considerably reduced, which is especially desirable; when thick deposits are being produced. high current densities, variation in rate of deposit is eifectively prevented because of the substantially constant conditions maintained in the solution. It has been found that as the propor-,

tion of sodium fluoride is increased above grams per litre, thesolubility of the ferrous sulphate is correspondingly reduced, which has the because of the use ofa current density of amperes -purities of course ,quality of greatly minimized by the invention,

, erating at a solution at 20 centigrade) solution at that concentration. Another factor is Moreover, even. at those -thateo effect of diminishing the range of current densities that may be satisfactorily employed.

Because of the presence of hydrofluoric acid in the solution, any ferric saltwith which the ferrous sulphate employed may have been contaminated, is immediately dissolved by reduction to the ferrous state, and during electrolysis any ferric salt which, because of oxidation of ferrous iron, may tend to precipitate out of the solution, is also reduced to the ferrous state, whereby the solution is maintained'clear at all times. Hitherto the precipitation of basic iron salts has been the source of considerable diflicultyin some electrolytes. Thus. these insoluble salts, if allowed to accumulate in the solutionpcause rough deposits, as well as inclusionsin such deposits, and must therefore be removed as fast as they are formed, as by continuously circulating the electrolyte through a suitable filter. Not only is the solution of the invention free from suspended particles and sediment at any time, but the necessity of continuous filtration is entirely eliminated.

As already stated, the solution of the invention is preferably operated at a pH ranging between 3.0 and 5.0. These low acidities are 'made possible hydrofluoric acid as the active acid reagent, complex ions being formed in the solution. And they may be used even when high densities of current are passed through the solution. Satisfactory deposits have thus been obtained from electrolytes operated within the preferred range of pH values specified and at per square decimeter.

Several advantages are obtained as a result of the low acidity values of the solution'which may be employed. One advantage is that the amount of hydrogen generated at the cathode is reduced to a minimum, which prevents the formation of brittle deposits normally caused by absorption of hydrogen. Another. advantage is that the use of expensive dlaphragms, such as asbestos bags or specially made porous pots, which has hitherto been required for collecting the insoluble impurias graphitic carbon, from the anodes, is eliminated. That is, simple canvas bags may be used to enclose the anodes. the collected imsettling to the bottom of such bags so that they in no way hinder anode corrosion. Moreover, the use of elaborate ventilating systems and of expensive containers for containing the solution is also eliminated.

It is well known that the pH of an electrolyte is apt to changedue to varying anodic conditions or other causes, such as accidental contamination with alkall'or acid, and that such changes have a marked effect on the current efliciency and the the deposits. These there beins several factors contributing to this effect. One factor has already been stated, namely, the even and quantitative solution at the anodes when opconcentration corresponding to a specific gravity of 1.25 (referred to water which factor maintains the the action of the sodium fluoride in the solution. That is, the sodium fluoride acts as a buffer salt controlling the pH of the solution against any great variation due to any cause. It is to be particularly noted, however, that this buffer action is almost entirely eliminated in solutions .havin! a degree of concentration appreciably less than rrespondlni to a specific gravity of 1.25 (referred to water at- 20 centigrade) changes are nickel to be deposited) "9,151.42 In the practice or theinventlon, it has been found that, due to the fact that the iron. and

nickel in the-anodes is completely dissolved, pe-

riodic. cleaning ofthe anodes is unnecessary.

there'being no formationof insoluble coatings on 25 gramsper litre of water, is then added to the water and dissolved therein; and, for thepurpose of forming hydrofluoric acid, there is "admixed with the resulting solution anfamount of-concentrated sulphuric acid (66 Baum) precalculated in the approximate proportion of 2 cubic centi meters per litre of water. Bags of ferrous-sub. phate are then suspended in the solution and are maintained therein until sufllcientferrousfisulphate has been dissolved to bring the specific gravity of the solution to 1.251(referred'to water at 20 centigrade), at the temperature of 70 centigrade. Upon removal of the ferrous sulphate bags, the solution is analyzed for its iron content, and the required amount of nickel sulphate based on this analysis is added to. cause the ratio of nickel to iron in the solution to be the same as in the desired alloy not substantially exceeding 5% nickel to be deposited. Thereafter, iron and nickel anodes eachcontaining these metals in the proper ratio of nickelto iron (also the same as in the desired alloy not substantially exceeding 5% are suspended in the solution, canvasbags being employed to enclose the anodes. The object or objects to be electroplated are likewise operatively positioned in the solution; and, at the temperature of 70 centigrade, the anode and cathode terminal bars are connected to an electroplating generator of suitable capacity.

whether it is n to add so-called addition reagents to correct the solution to the pH value desired. That is, an acidic correcting substance should be added ii the acid ity ofthe solution is to be increased, and an alkaline correcting substance should be added if the acidity of the solution is to be decreased. By

this means, if necessary, the pH of the solution is preferably adjusted to substantially 3.4, as measured by colorimetric methods, this pH value having been found'most satisfactory when the solution is operated at the temperature-of 70' centigrade and the specific gravitymf 1.25 (referred to water at 20 centigrade);

Sulphuric acid may be used as the acidic correcting substance, and sodium or ammonium hydroxide as the alkaline correctingsilbstance. .As to the current density which may be employed, amperes per square decimeter will produce satisfactory deposits of iron and nickel alloy not sub-,

stantially exceeding 5% nickel for building up worn machine parts and for electroforming.

When it is necessary to employ correcting substances, it has been found that if they are added to the. solutionby merely pouring them into the tank, they do not mix satisfactorily, thereby causing a detrimental localized condition to exist until the solution'is stirred thoroughly. This dim: culty can be overcome by employing a lead pipe objects being electroplated; This method of adding the correcting substances eliminates the necessity of removing the object or objects-being electroplated for the purpose of adjusting the solution. a

el alloy according'to theprocess of the present invention has been herein described as" being carried out from anodes each containing both iron and nickel, it is understood that the iron may 'be' deposited from separate anodes containing iron, and the nickel from separate anodes containing nickel.

of the solution substantially constant by adding nickel sulphate thereto at regular intervals, or to employ nickel anodes only and maintain the iron content of the Moreover, it is possible to employ iron anodes only and maintain the nickel content solution substantially constant by adding ferrous sulphate thereto at regular inter-f vals. Still anothe'r'possibility would be to employ non-corrosive electrodes as the anodes, the iron and nickel contents of the solution being tion of both ferrous sulphate and nickel sulphate at regular intervals.

,None of the procedures described in detail should be interpreted as limiting the invention, these procedures being capable of being modified in many ways without departing from its spirit. What is claimed is:

' 1. The process of electrolytically depositing iron and nickel alloy not substantially exceeding 5% Jnickel, which comprises electroplating through a heated solution of iron and nickel salts consisting v of ferrous sulphate and nickel sulphate, said solu- A pH test of the solution should then be made in order to determine tlon containing hydrofluoric acid and sodium fluoride, the relative quantities of ferrous sulphate and nickel sulphate present in said solution being such as to cause the ratio of nickel to iron present in said solution to be the same as in the desiredalloy not substantially exceeding 5% nickel to be deposited, the quantity of ferrous sulphate-present in said solution being sufllcient to bring it at the temperature of operation to a .then maintained substantially constantbyraddireacting sodium fluoride and sulphuric acid therein, the sodium fluoride'being employed in excess of the quantity required for the reaction.

the relative quantities. of ferrous sulphate and nickel sulphate present in said solution beingsuch as to cause the ratio of nickelto iron present in said solution to be the same as in the'desired alloy not substantially exceeding 5% nickel to be i 15 Whereas the electrodeposition of iron and nicksaturated therewith.

3. The process of. electrolytically depositing iron and nickel alloy not substantially exceeding 5% nickel, which comprises electroplating through a heated solution termed by adding to water sodium fluoride in the proportion of 25 grams per litre or water, sulphuric acid in amount to form by reaction with sodium fluoride suflicient hydrofluoric acid to cause the solution to be operated at a pH ranging between 3.0 and 5.0, ferrous sulphate in amount to bring the solution at the temperature or operation to a specific gravity of substantially 1.25 reierred to water at centitto be the same as rade, and nickel sulphate in amount to cause he ratio of nickel to iron present in the solution in the alloy not substantially exceeding 5% nickel to be deposited.

$.The process of electrolytically depositing iron and nickel alloy substantially'not exceeding 5% nickel, which comprises electroplating through a heated solution Iormed by adding to water sodium fluoride in the proportion of grams-per litre of water, concentrated sulphuric acid subbring the solution I stantially in the proportion of 2 cubic centimeters per litre' of water, ferrous sulphate in amount to bring the solution at the temperature ofoperation to a speciflcgravlty of substantially 1.25 referred to water at 20 centigrade, and nickel sulphate in amount to cause the ratio of nickel to iron present in the solution to be the same as in the desired alloy not substantially exceeding 5%.nickelto be deposited, said solution being maintained during operation. at a pH of substantially 3.4.

5. The proces of electrolytically depositing iron and nickel alloy not substantially exceeding 5% nickel, which comprises electroplating through a heated solution formed by addingto water sodium fluoride in the proportion of 25 grams per litre of water, concentrated sulphuricacid substantially in the proportion of 2 cubic centimeters per litre of water, ferrous sulphate in amount to at'the temperature of .operation to a'speciflcgravity of 1.25 referred to water at 20 centigrade, and nickel sulphate in amount to cause the ratio of nickel to iron present in the solution tovv be the same as in the desired alloy not substantially exceeding 5% nickel to be deposited, said solution being operated at a temperature of substantially 70 centlgrade, at a pH ranging between 3.0 and 5.0, and at a current density ranging between 15- and amperes per square decimeter.

WIILIAM A. CROWDER. 

